The invention relates to an internal combustion engine having a valve actuation device, wherein the internal combustion engine has at least one first exhaust valve and one second exhaust valve per cylinder, which can be actuated jointly in at least one operating range of the internal combustion engine via an exhaust valve bridge and a first valve lever by a first cam lobe of a first exhaust cam arranged on a camshaft.
Furthermore, the invention relates to a method for operating an internal combustion engine having at least one first exhaust valve and one second exhaust valve per cylinder, which are jointly actuated in at least one operating range via an exhaust valve bridge and a first valve lever by a first cam lobe of a first exhaust cam arranged on a camshaft.
It is known that in an internal combustion engine its own engine brake valve is arranged in addition to the exhaust valves, which is opened in a clocked or constant manner during engine braking. Such engine brake valves are usually operated hydraulically or pneumatically and are known, for example, from DE 44 23 657 C2, DE 38 39 452 C2, DE 38 39 450 C2, AT 004.387 U1 or AT 003.600 U1. An engine braking device is also known from DE 41 25 831 A1 whose engine brake valve is operated electrically.
Known actuation devices for engine brake valves, however, require a relatively high construction effort and need a comparatively large amount of space in the cylinder head, which in many cases is difficult to provide. To release the cylinder pressure, an additional tank and a high-pressure oil system with high-pressure pump and electro-hydraulic valves are usually required for each cylinder. In addition, well-known engine braking devices have a high number of individual parts which increase the susceptibility to faults and have a disadvantageous effect on the production effort.
U.S. Pat. No. 6,000,374 A describes an engine brake for an internal combustion engine in which several braking phases can be implemented per working cycle. In this case, in addition to intake and exhaust rocker arms, an additional brake rocker arm is provided for each cylinder, which—driven by a brake cam—actuates an exhaust valve. All rocker arms have a hydraulic element at their valve end. Solenoids can be used to influence which hydraulic elements are pressurized with pressure oil and which are not. This ensures that during normal working mode the brake rocker arm only runs empty and the exhaust valve is not actuated via the brake rocker arm because its hydraulic element cannot transmit the force without oil supply. The intake and exhaust rocker arms operate in working mode as long as their hydraulic elements are filled with oil. In braking mode, the hydraulic elements of the exhaust rocker arms are deactivated and the hydraulic elements of the brake rocker arms are activated. In this way it is also possible to manipulate the valve movements hydraulically in order to ensure brake power control and adaptation to any speed. The disadvantage is that a high level of control effort is required.
From WO 2015/177127 A1 a valve train is known for an internal combustion engine, which has per cylinder a first and a second exhaust valve, which can be operated via a valve bridge and a first valve lever by a first exhaust cam together. The second exhaust valve can also be actuated by a second exhaust cam to implement an engine brake via a second valve lever, with a hydraulic transmission device being arranged between the second valve lever and the second exhaust valve. Both the first and the second exhaust cams are connected to a camshaft in a torque-proof manner. The engine brake is activated or deactivated by the hydraulic transmission device.
In addition, the publications U.S. Pat. No. 9,188,030 B2, DE 10 2014 225 054 A1, DE 10 2010 023 571 A1 and WO 11/032632 A1 provide variable valve actuation devices for internal combustion engines in which the control time can be adjusted by relative rotation of two cams of a camshaft. EP 1 945 918 B1 also features a camshaft assembly comprising an inner shaft and an outer shaft, wherein the inner shaft is disposed within the outer shaft rotatable relative to the outer shaft. A first group of cams is connected to the outer tube in a torque-proof manner, a second group of cams is connected to the inner tube in a torque-proof manner.
It is the object of the invention to enable a rapid warm-up of an internal combustion engine of the type mentioned above as simply as possible. Another object is to make it as easy as possible for the exhaust aftertreatment system of such an internal combustion engine to start quickly.